Conventionally, a range image sensor which images an image including range information to a target is known. In this range image sensor, a method for acquiring range information by detecting a time of flight (TOF) since light is irradiated onto a target until reflected light is received, has been mainly adopted. This method includes two typical methods, and in one of the methods, the time of flight is measured and acquired, and in the other method, the time of flight is acquired by measuring a phase difference between light irradiated by using periodically modulated light and reflected light.
As a range image sensor using the latter method, one is known which includes a semiconductor substrate of a first conductive type, a first semiconductor region of a second conductive type which forms p-n junction with the semiconductor substrate, and a second semiconductor region of a second conductive type which is adjacent to the first semiconductor region and forms p-n junction with the semiconductor substrate (for example, refer to Patent Document 1).
In such a range image sensor, by applying different reverse bias voltages respectively between the first and second semiconductor regions adjacent to each other and the semiconductor substrate, the sizes of the depleted layers expanding from the p-n junctions of the first and second semiconductor regions are controlled. Then, light is irradiated from the light source toward a target, and reflected light is received, and accordingly, as shown in FIG. 8, an output signal of this reflected light is detected in a time sharing manner as output signals 53 and 54 from the first and second semiconductor regions. At this time, the output signal 54 from the second semiconductor region corresponds to a phase difference D0 between the brightness 55 of the light source and the brightness 56 of the reflected light, and corresponds to the time of flight. Therefore, by detecting the output signal 54 from the second semiconductor region, the time of flight is detected, and range information of the target is acquired.    Patent Document 1: Japanese Translation of International Application No. 2004-525351